Chapter 5, Problem 84GQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# Camping stoves are fueled by propane (C3H8), butane [C4H10(g), ΔfH° = –127.1 kJ/mol]. gasoline. or ethanol (C2H5OH). Calculate the enthalpy of combustion per gram of each of these fuels. [Assume that gasoline is represented by isooctane, C8H18(ℓ), with ΔfH° = –259.3 kJ/mol.) Do you notice any great differences among these fuels? How are these differences related to their composition?

Interpretation Introduction

Interpretation:

The enthalpy of combustion per gram of propane and butane has to be calculated

Concept Introduction:

The standard enthalpy change of combustion of a compound is the enthalpy change which occurs when one gram of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state

ΔrH0=ΣnΔfH0(products)-ΣnΔfH0(reactants)

The change in enthalpy, ΔH in kJ per mole of a given reactant for the reaction can be calculated as:

ΔrH=enthalpy changenumber of moles

ΔH=ΔrH×number of moles

Explanation

For propane the balanced equation is as follows:

â€‚Â C3H8+Â 5Â O2â†’â€‰3CO2+Â 4Â H2O

Î”rH0=[(3molÃ—-393.5kJ/mol)â€‰+(4molÃ—-285.83kJ/mol)]-[(1molÃ—-104.7Â kJ/mol+0)]

Î”rH0=-2219.12kJ

The change in enthalpy, Î”H in kJ per mole of a given reactant for the reaction can be calculated as:

â€‚Â Î”rH=enthalpyÂ changenumberÂ ofÂ molesÂ

â€‚Â Î”rH=-2219.12kJ/molâ€‰Ã—1mol44.1g=-50.32â€‰J/g.K

So, the enthalpy of combustion is -50.32â€‰J/g

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